With mobile subscribers increasing every day, it emerges as a requirement for to modern mobile communication systems to maintain high quality while enlarging the communication capacity. Among such attentions, smart antenna arises as a key technology in modern mobile communication fields.
Smart antenna technology, also known as antenna array technology, usually employs two or more single antenna elements to form an antenna array. When smart antenna used, appropriate weight factors are used to adjust the phase and amplitude of the signals received by each antenna element, thereby the desired signals are enhanced and the interference signals are suppressed after the received signals are weighted and summed. The essence of weight is a kind of spatial filtering.
Researches indicate the introduction of smart antennas can effectively increase SNR (Signal to Noise Ratio) of signals and thus greatly improve the communication quality during communication process. However, mobile terminals of current communication systems generally use the processing module for single antenna systems. If smart antenna technology is to be applied in present mobile terminals, both the hardware and the software of the processing module need to be redesigned, which can be very expensive. Therefore, how to make modifications based on present mobile terminals and take full advantage of the hardware and software resources of the processing module of single antenna systems, comes as a key issue for smart antennas to be applied in mobile terminals.
Now an example of a mobile terminal based on TD-SCDMA standard will be given to show the makeup of the single antenna system in current mobile terminals and the challenges smart antenna faced when applied to the said single antenna system.
FIG. 1 is a block diagram for a standard mobile phone with single antenna, comprising antenna 100, RF module 101, ADC/DAC module 102, baseband physical layer processing module 103, baseband control module 104 and baseband higher layer processing module 105, wherein baseband physical layer processing module 103 may be composed of Rake receiver, spreading/de-spreading module, modulating/demodulating module and Viterbi/Turbo coding/decoding module; while baseband higher layer processing module 105 may be composed of source coder/decoder.
In the downlink, radio signals received by antenna 100 are first amplified and down-converted to intermediate frequency (IF) signals or analog baseband signals in RF module 101; then the intermediate frequency signals or analog baseband signals are transformed to digital baseband signals to be inputted to baseband physical layer processing module 103, after being sampled and quantified in ADC/DAC module 102; in baseband physical layer processing module 103, depending on the control signals from baseband control module 104, signals obtained by successive operations such as Rake receiving, de-spreading, demodulating, deinterleaving, JD (joint detection), Viterbi/Turbo decoding and etc, are provided to baseband higher layer processing module 105; in baseband higher layer processing module 105, the data processed by baseband physical layer processing module 103 will be further processed in data link layer, network layer or higher layer, including higher layer signaling processing, system controlling, source coding/decoding and etc.
At present, the above mobile phone technology with single antenna is very mature. Many manufacturers, including Philips, have developed sound chip-set solutions, where the function of the said baseband physical layer processing module 103 is generally realized by baseband MODEM based on ASIC (application specific integrated circuits).
Whereas the introduction of smart antenna technology into present mobile phones will totally change the settings of the whole baseband physical layer processing module, whose hardware and corresponding software, such as Rake receivers, de-spreading functions and etc, can hardly be utilized.
To reuse the standard baseband system design, Innovics Inc, an electronics equipment provider in L.A., Calif., provided a mobile phone device with smart antennas as shown in FIG. 2.
As shown in FIG. 2, SA (smart antenna) module 206 comprises antenna combiner 208 and combining control module 207, wherein combining control module 207 adjusts two groups of weights of antenna combiner 208, according to the feedback signals outputted from Rake receiver & de-spreading module 209 and Viterbi/Turbo decoder module 210, while antenna combiner 208 combines the inputted signals of the two channels by individually multiplying a group of weights, according to the control signal provided by combining control module 207.
In this solution, smart antenna module (SA module 206) and Rake receiver are separated, i.e. space diversity and time diversity are implemented separately, so the software of standard baseband processing system can be reused. However, since combining control module 207 in SA module 206 still needs dynamic feedback signals from Rake receiver & de-spreading module 209 and Viterbi/Turbo decoder module 210 to control and adjust the antenna combiner 208, while the interface between combining control module 207 and Rake receiver & de-spreading module 209 or Viterbi/Turbo decoder module 210 is not compatible with standard baseband physical layer processing module, therefore, the hardware of standard solutions, such as baseband physical layer processing module 103 and etc, can't be reused.
Hence, if the above solution of Innovics Inc were adopted, the design of standard systems has to be modified, that is the baseband physical layer processing module 103 has to be redesigned to support the said SA Module 206, which can be very difficult.
As described above, with regard to reusing the design of present mobile terminals, only reuse of the software design has been realized in prior art, but reuse of both the software and hardware has not been achieved. Therefore, how to make modifications based on present mobile terminals and effectively take advantage of the hardware and software resources in the processing module of single antenna systems, still remains as a problem to be settled for smart antennas to be applied in mobile terminals.